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Shuttle tank tests indicate pressure problems

By Kelly Young

The external fuel and boosters (pictured) originally scheduled to launch Atlantis will now return shuttle Discovery to flight

(Image&colon; NASA)

Space shuttle Discovery’s external fuel tank completed further tests to examine the problems with its valves and sensors discovered during a previous fuelling test. While the sensors were all successfully back in working order, the tests on Friday morning hinted that some problems were persisting with the tank’s pressurisation system.

During the first fuelling test, conducted on 14 April, two liquid hydrogen sensors, which act as fuel gauges during launch, did not work properly. And a pressure relief valve was triggered more times than expected. So NASA added instruments to those areas to measure what might have occurred.

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The hydrogen sensors worked properly during this test, but the tank re-pressurised 13 times, the same number as the first tanking test. It should normally happen just eight or nine times. If it had happened more than 13 times, engineers would begin to suspect a fuel leak.

Temperatures rising

Parsons says the culprit might be a device known as a diffuser. It is a mesh screen at the top of the liquid hydrogen tank, used to disperse the helium gas evenly to avoid “hot spots” in the fuel. In addition, the propellant temperature rose slightly during both tests. “It kind of points to something isn’t right,” Parsons told reporters.

On Tuesday, NASA intends to roll Discovery back into the massive Vehicle Assembly Building. There, they will take Discovery off this external tank and solid rocket boosters and put it on a new tank and booster set which had originally been scheduled to fly with Atlantis on its next mission.

Heaters have been added to the liquid oxygen feedline bellows area on the new tank to prevent ice build-up, which could cause a hazard on take-off. The decision to swap boosters had been taken before Friday’s battery of tests, so that both tanks could benefit from extra heaters before attempting a launch.

NASA may conduct a third fuelling test but, if they do, it would make it harder to make the 13 July to 31 July launch window if any unexpected problems arise, says Mike Leinbach, NASA launch director.

This will be the first space shuttle launch since the Columbia accident in 2003. During launch, a piece of foam insulation from the external tank hit Columbia’s left wing. Since the accident, NASA has tried to find ways to reduce the foam and ice that could fall from the tank during lift-off.